19 Jan
2022
19 Jan
'22
3:57 p.m.
> Jay, one thing you’re missing is that a maximum of 2 (and almost always 1) radar altimeter will be in use per airfield, as one aircraft will be landing at a time. I believe that Lady Benjamin may have conflated the radar altimeter on aircraft with the instrument landing system transmitters. On Wed, Jan 19, 2022 at 3:52 PM Jay Hennigan <jay@west.net> wrote: > On 1/19/22 01:53, Lady Benjamin Cannon of Glencoe, ASCE wrote: > > Jay, one thing you’re missing is that a maximum of 2 (and almost always > 1) radar altimeter will be in use per airfield, as one aircraft will be > landing at a time. > > Really? I was under the impression that radar altimeters were pretty > much always active during flight. If not, what triggers the "PULL UP - > TERRAIN" audible warnings that are often heard on CVR recordings just > before an airplane flies into cumulo-granite weather (mountains) miles > from an airport? > > If in fact they are only used for IFR approach, is there a lockout to > ensure that the radar is only active on approach? If pilots forget to > turn them off after landing, does the radar transmitter automatically > shut itself off? > > > Apparently some old gear has trouble with even a 500MHz guard band, > which I also find astonishingly bad for any time, but a lot of aviation > tech is truly from another century. > > This is absolutely horrible receiver design on equipment critical to > aviation safety and it's surprising that tighter specs weren't enforced. > That adjacent spectrum hasn't exactly been silent until now. It's been > in use for decades going way back to Bell System TD-2 microwave that at > one point criss-crossed the country. > > > They also have main lobes approx 80* wide so they still function when > the plane is in 40* of bank. > > That makes sense. > > -- > Jay Hennigan - jay@west.net > Network Engineering - CCIE #7880 > 503 897-8550 - WB6RDV >